fwiw, I was able to confirm plex unable to load dvd order on some test files for this series.
I don’t know if it is only this series, or affects other series as well.
It could be a temporary tvdb problem, or a plex problem.
I don’t know if it will get resolved before then, but they are already testing a new tv scanner, so we may have to wait until then for a fix.
you can review the announcement and test the new scanner @ New Plex Media Server TV show/series scanner and agent preview